A concern in designing robotic devices capable of locomotion is keeping the devices stable as they traverse different environments. In the case of some robots, this task may be, at least in part, inherently achieved by designing the robot to have a low center of mass and a large number of support points. As an example, a robot having four wheels and a low center of mass may be capable of traversing uneven terrains without tipping over.
In contrast, many walking robots such as bipeds modeled after humans and quadrupeds modeled after animals may have high centers of mass and an inherently unstable gait. For such robotic devices, effective and efficient locomotion may require some knowledge of the terrain ahead. Terrains that contain obstacles and uneven surfaces may cause such robots to tip, lose balance, and fall over if these obstacles are not properly identified and accounted for.